sd_booted — Test whether the system is running the systemd init system.
#include <systemd/sd-daemon.h>
| int sd_booted( | void ); | 
On failure, this call returns a negative errno-style error code. If the system was booted up with systemd as init system, this call returns a positive return value, zero otherwise.
This function is provided by the reference implementation of APIs for new-style daemons and distributed with the systemd package. The algorithm it implements is simple, and can easily be reimplemented in daemons if it is important to support this interface without using the reference implementation.
Internally, this function checks whether the
                /sys/fs/cgroup/systemd virtual file
                system is mounted, by comparing the st_dev value of
                the stat() data of
                /sys/fs/cgroup and
                /sys/fs/cgroup/systemd.
For details about the algorithm check the liberally licensed reference implementation sources: http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c resp. http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h
sd_booted() is implemented
                in the reference implementation's
                sd-daemon.c and
                sd-daemon.h files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                libsystemd-daemon
                pkg-config(1)
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source
                tree. For more details about the reference
                implementation see
                sd_daemon(7).
If the reference implementation is used as drop-in files and -DDISABLE_SYSTEMD is set during compilation this function will always return 0 and otherwise become a NOP.